Key Points
Key Points: Coordination and Integration in the Human Body
- Coordination - the process by which two or more organs interact and complement each other's functions to maintain homeostasis.
- Neural system - provides point-to-point connections for quick coordination.
- Endocrine system - provides chemical integration through hormones for slower coordination.
- Both systems jointly coordinate organ activities - e.g., during exercise, muscles, lungs, heart, and kidneys all work together to meet increased oxygen and energy demands.
Key Points: Neural System
- The neural system is made of specialised cells called neurons.
- Neurons detect, receive and transmit stimuli (signals).
- In lower invertebrates (like Hydra), the neural system is simple and forms a network.
- In insects, the neural system is more organised with the brain, ganglia and nerve tissues.
- In vertebrates, the neural system is highly developed and complex.
Key Points: Human Neural System
- The human neural system is divided into two parts - CNS (Central Neural System) and PNS (Peripheral Neural System).
- CNS - consists of the brain and spinal cord; it is responsible for information processing and control.
- PNS - consists of all nerves associated with the CNS. Afferent fibres carry impulses from organs/tissues → CNS; Efferent fibres carry impulses from CNS → organs/tissues.
- PNS is divided into the Somatic neural system (relays impulses from the CNS to skeletal muscles) and the Autonomic neural system (controls involuntary organs and smooth muscles).
- The autonomic neural system is further divided into the sympathetic and Parasympathetic neural systems.
- Visceral nervous system - part of PNS; network of nerves, fibres, ganglia and plexuses that transmit impulses between CNS and the viscera (internal organs).
Key Points: Neuron: Structural & Functional Unit
- A neuron is the structural and functional unit of the neural system, consisting of the cell body, dendrites and axon.
- Cell body - has cytoplasm, organelles and Nissl's granules (protein synthesis). Dendrites - transmit impulses towards the cell body.
- Axon - transmits impulses away from the cell body; ends in a synaptic knob containing neurotransmitters.
- Types based on structure - Multipolar (1 axon + 2+ dendrites; cerebral cortex), Bipolar (1 axon + 1 dendrite; retina), Unipolar (1 axon only; embryonic stage).
- Myelinated - covered by myelin sheath (Schwann cells); found in cranial and spinal nerves. Non-myelinated - no myelin sheath; found in autonomic and somatic neural systems.
- Gaps between two myelin sheaths = Nodes of Ranvier.
- Types based on function - Sensory (receptors → CNS), Motor (CNS → muscles/glands), Association/Interneurons (within CNS).
Key Points: Generation and Conduction of Nerve Impulse
- Neurons are excitable cells with polarised membranes. Nerve impulse = sum of mechanical, chemical and electrical disturbances caused by a stimulus.
- Resting potential - high K⁺ and negative proteins inside; high Na⁺ outside; outer surface = positive, inner = negative → polarised membrane.
- The sodium-potassium pump maintains the gradient - moves 3 Na⁺ out and 2 K⁺ in.
- Stimulus → membrane becomes permeable to Na⁺ → Na⁺ rushes in → polarity reverses → depolarisation → action potential (nerve impulse) generated.
- Action potential travels as a wave of depolarisation along the axon from one site to the next.
- After depolarisation, K⁺ diffuses out → resting potential restored → fibre ready for next impulse (repolarisation).
Key Points: Transmission of Impulses
- Synapse - junction between a presynaptic and postsynaptic neuron; may be separated by a gap called the synaptic cleft.
- Two types of synapses - Electrical synapse (membranes very close; electrical current flows directly; faster transmission; rare in humans) and Chemical synapse (separated by synaptic cleft; uses neurotransmitters).
- Axon terminals contain synaptic vesicles filled with neurotransmitters (e.g., Acetylcholine).
- When an impulse arrives at the axon terminal → synaptic vesicles move towards the membrane → fuse with the plasma membrane → neurotransmitters are released into the synaptic cleft.
- Neurotransmitters bind to specific receptors on the postsynaptic membrane → ion channels open → ions enter → new potential generated in the postsynaptic neuron.
- The new potential generated can be either excitatory or inhibitory.
Key Points: Central Neural System
- The Central Neural System (CNS) consists of the brain and spinal cord.
- The brain is the control centre of the body, managing voluntary and involuntary activities.
- It controls functions like balance, temperature, hunger, thirst, memory, emotions, and thinking.
- The brain is protected by the skull and three meninges (dura mater, arachnoid, pia mater).
- The brain is divided into forebrain, midbrain and hindbrain.
- Forebrain (cerebrum, thalamus, hypothalamus) controls thinking, sensory functions and body regulation.
- Hindbrain (cerebellum, pons, medulla) controls balance, coordination and involuntary actions like breathing and heartbeat.
